Electrically powered vehicles such as electric vehicles and hybrid vehicles have attracted a lot of attention as environmentally friendly vehicles. An electric vehicle has a vehicle-mounted battery charged by a power supply outside of the vehicle, and travels by driving a motor with the charged power. A hybrid vehicle incorporates a motor as well as an engine as a driving source, or additionally incorporates a fuel cell as a DC power supply for driving the vehicle.
As with an electric vehicle, a hybrid vehicle having a vehicle-mounted battery that can be charged by a power supply outside of the vehicle is known. For example, a so-called “plug-in hybrid vehicle” is known in which a vehicle-mounted battery can be charged by a power supply in an ordinary household by connecting a power supply outlet provided at the house to a charging inlet provided in the vehicle by a charging cable.
Wireless power transfer without using a power cord or a power transfer cable has been receiving attention in recent years as a method of transferring power. Power transfer using electromagnetic induction, power transfer using a microwave, and power transfer by resonance are known as dominant techniques for wirelessly transferring power.
Resonance is a technique for causing a pair of resonators (e.g., a pair of self-resonant coils) to resonate with each other in an electromagnetic field (near field) to transfer power in a non-contact manner through the electromagnetic field, and can transfer a large amount of power of several kW across a relatively long distance (e.g., several meters) (see Non-Patent Document 1).    Non-Patent Document 1: Andre Kurs et al., “Wireless Power Transfer via Strongly Coupled Magnetic Resonances,” [online], Jul. 6, 2007, Science, Vol. 317, pp. 83-86, [searched on Sep. 12, 2007], the Internet    <URL:http://www.sciencemag.org/cgi/reprint/317/5834/83.pdf>